Misfires can be caused by lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or many other causes. Even a small number of misfires may result in excessive exhaust emissions due to the unburned mixture. Increased misfire rates cause damage to the catalytic converter. The ECM/PCM monitors the crankshaft speed variation to determine if any misfiring generated. The ECM/PCM identifies the specific cylinder in which the misfire has occurred and counts individual misfire events by monitoring changes in the crankshaft rotation for each cylinder. A random misfire indicates one or more cylinders are misfiring.
If there happen misfires over the threshold value at #4 cylinder, ECM/PCM sets DTC P0304.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Engine roughness through crankshaft speed fluctuation | 1. Poor connection 2. Ignition system 3. Fuel system 4. Intake/exhaust air system 5. Ignition timing 6. Injector |
Enable Conditions |
•
Time after engine start > 25s
•
No CKP sensor error
•
No rough road condition
•
No fuel cut off condition | |
Threshold Value |
•
Misfire rate / cylinder > 3% of total misfire rate (emission threshold)
•
Misfire rate / cylinder > 5~33% of total misfire rate (catalyst damage threshold) | |
Diagnostic Time |
•
Continuous | |
MIL ON Condition |
•
2 driving cycle or Immediately (Blink) |
